Check valves are valves that allow fluid flow through a hydraulic passage only one direction. Check valves generally have an inlet port for allowing fluid flow in and an outlet port for allowing fluid to exit the valve. Check valves of the type disclosed herein work automatically and are controlled mainly by the pressure of fluid flow. They are available in a variety of sizes and are used in a wide variety of applications.
One such application is, for example, an intake check valve installed in a reciprocating pump which allows fluid flow into the pump's working chamber which is typically a piston cylinder. Such intake check valves allow fluid to flow into the working chamber, during the intake stroke, but prevent fluid from flowing out of the pump in the opposite direction, during the pump's power stroke. An example of such a pump is a reciprocating piston pump used to supply liquid natural gas (LNG) to a natural gas fuelled internal combustion engine.
Because check valves are actuated mainly by the fluid forces acting on the valve member, the constructional features of the check valve have to be designed such that the valve allows the pump to operate with a low net positive suction head (NPSH). In addition, in a pump, the quickness with which an intake check valve responds to open and close fluid flow, at the desired times, has an impact on the volumetric efficiency of the pump.
An intake check valve that uses a valve member in the shape of a flat disc, which allows fluid flow between the intake valve inlet and outlet when the valve member is lifted from its seat is known. The response time of the valve depends largely on the fluid force acting on it and the weight of the valve member when no actuation assisting components, such as elastic elements, are employed to help with opening of the check valve.
In larger check valves, for example in high capacity pumps that require high flow rates, to maintain an acceptable low pressure drop through the check valve, the inlet port of the pump is correspondingly larger and the dimensions of the intake check valve member has to also be increased. While the valve member of the intake check valve is designed with a weight that ensures an appropriate sealing between the valve member and its seat when the valve is closed, using a heavier valve member can affect the valve's response time.
Check valves have to fulfill other design requirements as well, such as a good sealing between the valve member and its seat when the valve is closed and being strong enough to withstand the different pressures acting on it, especially when the fluid in the pump's working chamber is being pressurized. Another feature of such check valves relates to prevent the sticking of the valve member to the valve seat, for example, for valves which handle fluids with contaminants which can adhere to the valve member. Such problems have been solved in the past by having a valve member with a convex surface as described in U.S. Pat. Nos. 7,484,526 and 8,328,543. In these examples, the convex surface of the valve member is facing the seat of the valve member to allow a better sealing and, respectively, to prevent the sticking of the valve member to the valve seat.
While the solutions from the prior art mentioned above address some of the problems related to the operation of different check valves, there is still a need for a simple solution for improving the response time of check valves, in particular of larger valves used for example in high capacity pumps and especially those pumps that are pumping fluids that are at a temperature near their boiling point, because a high pressure drop with such fluids can result in vaporization and reduced performance.